The present invention is especially directed to crushing apparatus in which material to be crushed is fed into the nip between the teeth of a pair of power-driven, counter-rotating rolls driven at different speeds to be crushed into relatively fine particles. In the usual case, the rolls are provided with somewhat intermeshing teeth which must act to drive incoming lumps into the nip. The teeth are so designed that the teeth on one roll do not contact the teeth on the other, but, as the teeth pass through the nip between the rolls, they approach their minimum spacing from each other, and it is this minimum spacing which defines the maximum size of particles which are crushed by their passage through the nip. U.S. Pat. Nos. which disclose such crushers are: 48,244, 842,681, 1,435,330, 1,750,941, 1,824,088, 2,578,540, 2,588,900, 3,208,677, 3,240,436, 3,474,973.
A typical operation employing crusher roll pairs of the type referred to above is found in foundries where used sand cores employed in the casting operations are crushed in order to salvage the sand for use in making up new cores.
Most presently available crusher rolls employed in operations of the type described above are found wanting from the standpoint of the range of reduction in size which they can achieve. Those roll pairs which will accept and positively feed relatively large lumps into the crushing nip will discharge relatively large sized crushed particles which are too large for their intended use, while those roll pairs which will crush particles to the desired degree of fineness will not adequately feed relatively large lumps. In the previously mentioned example of crushing foundry sand cores, the cores or parts thereof recovered are frequently of relatively large over-all dimension as compared to the size of the sand particle desired, and most core crushing operations require passage of the material through two or three or more successively finer pairs of crushing rolls before particles of the desired degree of fineness are obtained.
It is the purpose of the present invention to provide a tooth configuration for crushing rolls of the type described above which will accept material of relatively large over-all dimension and crush the material into relatively small particles so that objects, such as foundry sand cores, can be reduced to particles of the desired fineness in a single crushing operation. Whereas previous machinery has normally accomplished 6:1 reduction, the present construction is designed to greatly exceed this.